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<pre><span class="sourceLineNo">001</span>/*<a name="line.1"></a>
<span class="sourceLineNo">002</span> * Copyright (C) 2007 The Guava Authors<a name="line.2"></a>
<span class="sourceLineNo">003</span> *<a name="line.3"></a>
<span class="sourceLineNo">004</span> * Licensed under the Apache License, Version 2.0 (the "License");<a name="line.4"></a>
<span class="sourceLineNo">005</span> * you may not use this file except in compliance with the License.<a name="line.5"></a>
<span class="sourceLineNo">006</span> * You may obtain a copy of the License at<a name="line.6"></a>
<span class="sourceLineNo">007</span> *<a name="line.7"></a>
<span class="sourceLineNo">008</span> * http://www.apache.org/licenses/LICENSE-2.0<a name="line.8"></a>
<span class="sourceLineNo">009</span> *<a name="line.9"></a>
<span class="sourceLineNo">010</span> * Unless required by applicable law or agreed to in writing, software<a name="line.10"></a>
<span class="sourceLineNo">011</span> * distributed under the License is distributed on an "AS IS" BASIS,<a name="line.11"></a>
<span class="sourceLineNo">012</span> * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.<a name="line.12"></a>
<span class="sourceLineNo">013</span> * See the License for the specific language governing permissions and<a name="line.13"></a>
<span class="sourceLineNo">014</span> * limitations under the License.<a name="line.14"></a>
<span class="sourceLineNo">015</span> */<a name="line.15"></a>
<span class="sourceLineNo">016</span><a name="line.16"></a>
<span class="sourceLineNo">017</span>package com.google.common.util.concurrent;<a name="line.17"></a>
<span class="sourceLineNo">018</span><a name="line.18"></a>
<span class="sourceLineNo">019</span>import com.google.common.annotations.VisibleForTesting;<a name="line.19"></a>
<span class="sourceLineNo">020</span>import com.google.common.base.Preconditions;<a name="line.20"></a>
<span class="sourceLineNo">021</span>import com.google.common.collect.Lists;<a name="line.21"></a>
<span class="sourceLineNo">022</span><a name="line.22"></a>
<span class="sourceLineNo">023</span>import java.util.Queue;<a name="line.23"></a>
<span class="sourceLineNo">024</span>import java.util.concurrent.Executor;<a name="line.24"></a>
<span class="sourceLineNo">025</span>import java.util.logging.Level;<a name="line.25"></a>
<span class="sourceLineNo">026</span>import java.util.logging.Logger;<a name="line.26"></a>
<span class="sourceLineNo">027</span><a name="line.27"></a>
<span class="sourceLineNo">028</span>/**<a name="line.28"></a>
<span class="sourceLineNo">029</span> * &lt;p&gt;A list of listeners, each with an associated {@code Executor}, that<a name="line.29"></a>
<span class="sourceLineNo">030</span> * guarantees that every {@code Runnable} that is {@linkplain #add added} will<a name="line.30"></a>
<span class="sourceLineNo">031</span> * be executed after {@link #execute()} is called. Any {@code Runnable} added<a name="line.31"></a>
<span class="sourceLineNo">032</span> * after the call to {@code execute} is still guaranteed to execute. There is no<a name="line.32"></a>
<span class="sourceLineNo">033</span> * guarantee, however, that listeners will be executed in the order that they<a name="line.33"></a>
<span class="sourceLineNo">034</span> * are added.<a name="line.34"></a>
<span class="sourceLineNo">035</span> *<a name="line.35"></a>
<span class="sourceLineNo">036</span> * &lt;p&gt;Exceptions thrown by a listener will be propagated up to the executor.<a name="line.36"></a>
<span class="sourceLineNo">037</span> * Any exception thrown during {@code Executor.execute} (e.g., a {@code<a name="line.37"></a>
<span class="sourceLineNo">038</span> * RejectedExecutionException} or an exception thrown by {@linkplain<a name="line.38"></a>
<span class="sourceLineNo">039</span> * MoreExecutors#sameThreadExecutor inline execution}) will be caught and<a name="line.39"></a>
<span class="sourceLineNo">040</span> * logged.<a name="line.40"></a>
<span class="sourceLineNo">041</span> *<a name="line.41"></a>
<span class="sourceLineNo">042</span> * @author Nishant Thakkar<a name="line.42"></a>
<span class="sourceLineNo">043</span> * @author Sven Mawson<a name="line.43"></a>
<span class="sourceLineNo">044</span> * @since 1.0<a name="line.44"></a>
<span class="sourceLineNo">045</span> */<a name="line.45"></a>
<span class="sourceLineNo">046</span>public final class ExecutionList {<a name="line.46"></a>
<span class="sourceLineNo">047</span><a name="line.47"></a>
<span class="sourceLineNo">048</span>  // Logger to log exceptions caught when running runnables.<a name="line.48"></a>
<span class="sourceLineNo">049</span>  @VisibleForTesting static final Logger log =<a name="line.49"></a>
<span class="sourceLineNo">050</span>      Logger.getLogger(ExecutionList.class.getName());<a name="line.50"></a>
<span class="sourceLineNo">051</span><a name="line.51"></a>
<span class="sourceLineNo">052</span>  // The runnable,executor pairs to execute.<a name="line.52"></a>
<span class="sourceLineNo">053</span>  private final Queue&lt;RunnableExecutorPair&gt; runnables = Lists.newLinkedList();<a name="line.53"></a>
<span class="sourceLineNo">054</span><a name="line.54"></a>
<span class="sourceLineNo">055</span>  // Boolean we use mark when execution has started.  Only accessed from within<a name="line.55"></a>
<span class="sourceLineNo">056</span>  // synchronized blocks.<a name="line.56"></a>
<span class="sourceLineNo">057</span>  private boolean executed = false;<a name="line.57"></a>
<span class="sourceLineNo">058</span><a name="line.58"></a>
<span class="sourceLineNo">059</span>  /** Creates a new, empty {@link ExecutionList}. */<a name="line.59"></a>
<span class="sourceLineNo">060</span>  public ExecutionList() {<a name="line.60"></a>
<span class="sourceLineNo">061</span>  }<a name="line.61"></a>
<span class="sourceLineNo">062</span><a name="line.62"></a>
<span class="sourceLineNo">063</span>  /**<a name="line.63"></a>
<span class="sourceLineNo">064</span>   * Adds the {@code Runnable} and accompanying {@code Executor} to the list of<a name="line.64"></a>
<span class="sourceLineNo">065</span>   * listeners to execute. If execution has already begun, the listener is<a name="line.65"></a>
<span class="sourceLineNo">066</span>   * executed immediately.<a name="line.66"></a>
<span class="sourceLineNo">067</span>   *<a name="line.67"></a>
<span class="sourceLineNo">068</span>   * &lt;p&gt;Note: For fast, lightweight listeners that would be safe to execute in<a name="line.68"></a>
<span class="sourceLineNo">069</span>   * any thread, consider {@link MoreExecutors#sameThreadExecutor}. For heavier<a name="line.69"></a>
<span class="sourceLineNo">070</span>   * listeners, {@code sameThreadExecutor()} carries some caveats: First, the<a name="line.70"></a>
<span class="sourceLineNo">071</span>   * thread that the listener runs in depends on whether the {@code<a name="line.71"></a>
<span class="sourceLineNo">072</span>   * ExecutionList} has been executed at the time it is added. In particular,<a name="line.72"></a>
<span class="sourceLineNo">073</span>   * listeners may run in the thread that calls {@code add}. Second, the thread<a name="line.73"></a>
<span class="sourceLineNo">074</span>   * that calls {@link #execute} may be an internal implementation thread, such<a name="line.74"></a>
<span class="sourceLineNo">075</span>   * as an RPC network thread, and {@code sameThreadExecutor()} listeners may<a name="line.75"></a>
<span class="sourceLineNo">076</span>   * run in this thread. Finally, during the execution of a {@code<a name="line.76"></a>
<span class="sourceLineNo">077</span>   * sameThreadExecutor} listener, all other registered but unexecuted<a name="line.77"></a>
<span class="sourceLineNo">078</span>   * listeners are prevented from running, even if those listeners are to run<a name="line.78"></a>
<span class="sourceLineNo">079</span>   * in other executors.<a name="line.79"></a>
<span class="sourceLineNo">080</span>   */<a name="line.80"></a>
<span class="sourceLineNo">081</span>  public void add(Runnable runnable, Executor executor) {<a name="line.81"></a>
<span class="sourceLineNo">082</span>    // Fail fast on a null.  We throw NPE here because the contract of<a name="line.82"></a>
<span class="sourceLineNo">083</span>    // Executor states that it throws NPE on null listener, so we propagate<a name="line.83"></a>
<span class="sourceLineNo">084</span>    // that contract up into the add method as well.<a name="line.84"></a>
<span class="sourceLineNo">085</span>    Preconditions.checkNotNull(runnable, "Runnable was null.");<a name="line.85"></a>
<span class="sourceLineNo">086</span>    Preconditions.checkNotNull(executor, "Executor was null.");<a name="line.86"></a>
<span class="sourceLineNo">087</span><a name="line.87"></a>
<span class="sourceLineNo">088</span>    boolean executeImmediate = false;<a name="line.88"></a>
<span class="sourceLineNo">089</span><a name="line.89"></a>
<span class="sourceLineNo">090</span>    // Lock while we check state.  We must maintain the lock while adding the<a name="line.90"></a>
<span class="sourceLineNo">091</span>    // new pair so that another thread can't run the list out from under us.<a name="line.91"></a>
<span class="sourceLineNo">092</span>    // We only add to the list if we have not yet started execution.<a name="line.92"></a>
<span class="sourceLineNo">093</span>    synchronized (runnables) {<a name="line.93"></a>
<span class="sourceLineNo">094</span>      if (!executed) {<a name="line.94"></a>
<span class="sourceLineNo">095</span>        runnables.add(new RunnableExecutorPair(runnable, executor));<a name="line.95"></a>
<span class="sourceLineNo">096</span>      } else {<a name="line.96"></a>
<span class="sourceLineNo">097</span>        executeImmediate = true;<a name="line.97"></a>
<span class="sourceLineNo">098</span>      }<a name="line.98"></a>
<span class="sourceLineNo">099</span>    }<a name="line.99"></a>
<span class="sourceLineNo">100</span><a name="line.100"></a>
<span class="sourceLineNo">101</span>    // Execute the runnable immediately. Because of scheduling this may end up<a name="line.101"></a>
<span class="sourceLineNo">102</span>    // getting called before some of the previously added runnables, but we're<a name="line.102"></a>
<span class="sourceLineNo">103</span>    // OK with that.  If we want to change the contract to guarantee ordering<a name="line.103"></a>
<span class="sourceLineNo">104</span>    // among runnables we'd have to modify the logic here to allow it.<a name="line.104"></a>
<span class="sourceLineNo">105</span>    if (executeImmediate) {<a name="line.105"></a>
<span class="sourceLineNo">106</span>      new RunnableExecutorPair(runnable, executor).execute();<a name="line.106"></a>
<span class="sourceLineNo">107</span>    }<a name="line.107"></a>
<span class="sourceLineNo">108</span>  }<a name="line.108"></a>
<span class="sourceLineNo">109</span><a name="line.109"></a>
<span class="sourceLineNo">110</span>  /**<a name="line.110"></a>
<span class="sourceLineNo">111</span>   * Runs this execution list, executing all existing pairs in the order they<a name="line.111"></a>
<span class="sourceLineNo">112</span>   * were added. However, note that listeners added after this point may be<a name="line.112"></a>
<span class="sourceLineNo">113</span>   * executed before those previously added, and note that the execution order<a name="line.113"></a>
<span class="sourceLineNo">114</span>   * of all listeners is ultimately chosen by the implementations of the<a name="line.114"></a>
<span class="sourceLineNo">115</span>   * supplied executors.<a name="line.115"></a>
<span class="sourceLineNo">116</span>   *<a name="line.116"></a>
<span class="sourceLineNo">117</span>   * &lt;p&gt;This method is idempotent. Calling it several times in parallel is<a name="line.117"></a>
<span class="sourceLineNo">118</span>   * semantically equivalent to calling it exactly once.<a name="line.118"></a>
<span class="sourceLineNo">119</span>   *<a name="line.119"></a>
<span class="sourceLineNo">120</span>   * @since 10.0 (present in 1.0 as {@code run})<a name="line.120"></a>
<span class="sourceLineNo">121</span>   */<a name="line.121"></a>
<span class="sourceLineNo">122</span>  public void execute() {<a name="line.122"></a>
<span class="sourceLineNo">123</span>    // Lock while we update our state so the add method above will finish adding<a name="line.123"></a>
<span class="sourceLineNo">124</span>    // any listeners before we start to run them.<a name="line.124"></a>
<span class="sourceLineNo">125</span>    synchronized (runnables) {<a name="line.125"></a>
<span class="sourceLineNo">126</span>      if (executed) {<a name="line.126"></a>
<span class="sourceLineNo">127</span>        return;<a name="line.127"></a>
<span class="sourceLineNo">128</span>      }<a name="line.128"></a>
<span class="sourceLineNo">129</span>      executed = true;<a name="line.129"></a>
<span class="sourceLineNo">130</span>    }<a name="line.130"></a>
<span class="sourceLineNo">131</span><a name="line.131"></a>
<span class="sourceLineNo">132</span>    // At this point the runnables will never be modified by another<a name="line.132"></a>
<span class="sourceLineNo">133</span>    // thread, so we are safe using it outside of the synchronized block.<a name="line.133"></a>
<span class="sourceLineNo">134</span>    while (!runnables.isEmpty()) {<a name="line.134"></a>
<span class="sourceLineNo">135</span>      runnables.poll().execute();<a name="line.135"></a>
<span class="sourceLineNo">136</span>    }<a name="line.136"></a>
<span class="sourceLineNo">137</span>  }<a name="line.137"></a>
<span class="sourceLineNo">138</span><a name="line.138"></a>
<span class="sourceLineNo">139</span>  private static class RunnableExecutorPair {<a name="line.139"></a>
<span class="sourceLineNo">140</span>    final Runnable runnable;<a name="line.140"></a>
<span class="sourceLineNo">141</span>    final Executor executor;<a name="line.141"></a>
<span class="sourceLineNo">142</span><a name="line.142"></a>
<span class="sourceLineNo">143</span>    RunnableExecutorPair(Runnable runnable, Executor executor) {<a name="line.143"></a>
<span class="sourceLineNo">144</span>      this.runnable = runnable;<a name="line.144"></a>
<span class="sourceLineNo">145</span>      this.executor = executor;<a name="line.145"></a>
<span class="sourceLineNo">146</span>    }<a name="line.146"></a>
<span class="sourceLineNo">147</span><a name="line.147"></a>
<span class="sourceLineNo">148</span>    void execute() {<a name="line.148"></a>
<span class="sourceLineNo">149</span>      try {<a name="line.149"></a>
<span class="sourceLineNo">150</span>        executor.execute(runnable);<a name="line.150"></a>
<span class="sourceLineNo">151</span>      } catch (RuntimeException e) {<a name="line.151"></a>
<span class="sourceLineNo">152</span>        // Log it and keep going, bad runnable and/or executor.  Don't<a name="line.152"></a>
<span class="sourceLineNo">153</span>        // punish the other runnables if we're given a bad one.  We only<a name="line.153"></a>
<span class="sourceLineNo">154</span>        // catch RuntimeException because we want Errors to propagate up.<a name="line.154"></a>
<span class="sourceLineNo">155</span>        log.log(Level.SEVERE, "RuntimeException while executing runnable "<a name="line.155"></a>
<span class="sourceLineNo">156</span>            + runnable + " with executor " + executor, e);<a name="line.156"></a>
<span class="sourceLineNo">157</span>      }<a name="line.157"></a>
<span class="sourceLineNo">158</span>    }<a name="line.158"></a>
<span class="sourceLineNo">159</span>  }<a name="line.159"></a>
<span class="sourceLineNo">160</span>}<a name="line.160"></a>




























































</pre>
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